Excessive concentrations of perchlorate in the environment, and especially in water consumed by human is highly problematic as perchlorate is known to interfere with iodide uptake into the thyroid gland. Dysregulation of iodide uptake is often manifested in disruption of thyroid functions, leading to several problems, including impaired regulation of energy metabolism, problems associated with development of fetus and young children, and in some cases even promotion of tumor growth. Despite the known dangers of perchlorate, California has currently no established drinking water standard or maximum contaminant level (MCL) for perchlorate. Instead, the department of health and safety (DHS) refers to an action level for perchlorate of 6 micrograms per liter (μg/L), which is expected to become the MCL.
It is well known in the art to capture perchlorate from potable water using an anion exchange resin. However, resins are expensive and typically only concentrate and transfer the problem from the water source to the eluent. Moreover, many anion exchange resins will capture other anions, including sulfate, nitrate, and bicarbonate. To circumvent non-specific binding of other anions, perchlorate specific anion exchange resins may be used. For example, suitable anion exchange resins include SYBRON™ SR-6 and 7, LEWITT™ 6362, PUROLITE™ A 520E, A 530 E, A 600 E and A 850 E or Rohm & Haas' AMBERLITE™ PWA 2 and IMAC 555 HP.
Despite the relatively high selectivity of certain resins towards perchlorate, various difficulties nevertheless remain. Among other things, competing anions are often present in 100- to 1000-fold (and even higher) molar excess, and will therefore still capture substantial quantities of non-perchlorate anions. Consequently, most of these resins cannot be effectively regenerated by simple methods such as brine or caustic treatments, but require relatively cumbersome regeneration methods (e.g., high temperature and pressure treatment with tetrachloroferrate as described in U.S. Pat. No. 6,448,299 and U.S. Pat. Appl. 2003/0222031). Other methods, such as on-column destruction of perchlorate by an aqueous solution of titanium-(III)-oxalate complexes require addition of alcohols to accelerate the perchlorate destruction reaction, as described in U.S. Pat. No. 6,358,396. The use of titanium (III) to reduce perchlorate to chloride was also reported by Cope et al., J. Chem. Soc. A; 301 (1967), and again by Lui et al., Inorg. Chem. 23, 3418, (1984). Though attractive at first sight, such methods typically fail to remove sulfate and bicarbonate from the resin, as these methods will only reduce perchlorate to chloride. Thus, as neither carbonate, bicarbonate, nor sulfate are reducible with titanium (III), the exchange medium requires additional regeneration by alternative techniques to remove carbonate, bicarbonate, sulfate, and nitrate. Furthermore, the '396 patent teaches that organic chelating agents (e.g., oxalate) are necessary to stabilize the titanium (IV) and prevent hydrolysis to titanium dioxide. Consequently, such methods are of limited commercial value due to the relatively low concentrations of titanium (III) species used for the reaction, and the slow rate of reduction even at relatively high concentrations of perchlorate ions.
Electrochemical generation and regeneration of Ti (III) from Ti (IV) in sulfuric acid and methanesulfonic acid are described respectively by Bandlish in U.S. Pat. No. 5,266,173 and Harrison in U.S. Pat. Nos. 5,246,553, 5,409,581, and 5,679,235. In these patents, titanium (III) is used for the mediated electro-organic synthesis of aromatic amines and other compounds. Foller et al also describe in U.S. Pat. No. 5,250,162 the electrochemical generation of Ti (III) in the context of the manufacture of titanium dioxide.
Therefore, although numerous methods and configurations for perchlorate destruction are known in the art, all or almost all of them suffer from one or more disadvantages. Consequently, there is still a need to provide improved compositions, methods and devices for perchlorate destruction.